Both sides are under pressure: the opposition from fear of more state-sponsored violence and long-time President Robert Mugabe from widening Western sanctions.

The US broadened its sanctions against targeted Zimbabweans and their companies, calling Mugabe's an "illegitimate" and "brutal" regime.

South African presidential spokesman Mukoni Ratshitanga said the Zimbabwean talks got "fully under way" on Thursday and were "continuing and they are proceeding well"

Mugabe's ruling Zanu-PF party and Morgan Tsvangirai's opposition Movement for Democratic Change have committed themselves to negotiating "an inclusive government" within two weeks.

The Zimbabwe parties also agreed to negotiate a slew of other issues, including revival of the shattered economy and a new constitution - but most points already had been negotiated at talks that broke off in January, ahead of presidential and legislative elections.

The biggest obstacle is agreeing on who will lead a new government.

"The opposition wants to be in the driving seat. The only way for the economy to be handled is for Mugabe to withdraw altogether, and I don't see that happening," said John Makumbe, a political analyst at the University of Zimbabwe. "I see the whole thing collapsing or, if a deal is reached, it will look so bad no one will accept it."

But the resilient Mugabe, who has survived years of attempts to oust him even by his own party, insists that he should head any government.

Tsvangirai says he won the most votes at the only legitimate election in March. But he did not win enough to avoid a runoff, from which he belatedly withdrew because of mounting state violence against his supporters. Mugabe ran alone in the June runoff and declared himself victor, though most of the world sees that election as a sham.